ISOTHIOCYANATES FORMED DURING ACCELERATED VULCANIZATION - PART 2 - GUANIDINE ACCELERATORS

During sulfur vulcanization accelerated by guanidines (OTBG, DPG, DOTG ) isothiocyanates (ITC) are formed inevitably. ITC are obtained both b y splitting of thiourea originated from guanidines and by reaction of primary amines with CS, (COS) donating compounds. The mechanism of the ITC formation was studied on unfilled IR compounds vulcanized at 180 and 210 degrees C. The reaction products were analysed by GC/MS and HP LC/MS. Increasing sulfur dosage and higher vulcanization temperature p romote the emission of ITC, Among the guanidines the highest amount of ITC is formed with OTBG. By addition of thiurams to the guanidine mix tures the amount of ITC increases frequently. Against that, MBT as sec ondary accelerator causes a retarding effect. Especially with OTBG/MBT -mixtures the lowest amounts of ITC are reached, Therefore small chang es to either formulation or processing conditions can significantly re duce ITC in fumes.